4.3 Axicon systems

Some systems use CO laser beams focused by a conical lens. This configuration, called “axicon”,
generates a ring-shaped intensity profile on the mirror. We do not attempt to compute an analytical model
of the compensation power flow. We use numerical intensity measurements carried out by the Virgo/Rome
team [15]. The FB coefficients of the optical power flow are computed numerically. The profile of the
corresponding thermal lens can be seen in Figure 31.